The present invention relates to key-operated, electronic musical instruments and more particularly to an improved gate circuit for use in such instruments.
In key-operated electronic musical instruments (such as electronic organs) it is desirable to reduce the number of mechanical contacts necessary to generate sounds to a minimum, preferably one contact per key. To this end, gate circuits are utilized so that upon the depression of any particular key, an output signal is generated for subsequent processing to develop the desired tone. The output signal appears at the output of a gate the inputs to which are a first, continuous voltage which is present at all the gates and a key-supplied voltage which is applied to the gate in response to the depression of a particular key. The output signal absolute value should correspond to the steady-state (quiescent) condition value of the continuous voltage.
While the above described arrangement is presently utilized, it suffers from a serious drawback. Namely, the tone signal and the key voltage influence each other. That is, the signal voltage that develops in response to the depressions of a key has an average value upon which a sound dependent signal is superimposed. As the amplitude of the one ac- signal increases, the average value of the signal voltage also necessarily increases (to a value above that of the steady-state condition value). This increase is known as "bounce".
Heretofore, various schemes and circuits have been developed to eliminate bounce. In the main, these schemes have sought to increase the common supply voltage to the transistor gates in response to the development of a key-induced voltage in such a way that the average value of the continuous voltage corresponds to the output voltage. To this end, the common supply voltage is provided by a regulator whose input is connected to the top of a voltage divider. The keys (which supply the key voltage) connect suitable resistors in parallel with the elements of the voltage divider to alter the value of the supply voltage. Such circuits are expensive and do not permit all the gates to operate with a uniform supply voltage since it has been found that satisfactory compensation cannot be achieved by this method where different filters are used in the further signal processing stages. In many such electronic organs, the different foot pedals control different filters for subsequent processing. Also, for a particular foot position, in many instances, the gates of neighboring keys are grouped together (e.g., in octaves) and connected to different filters.
In view of the above, it is the principal object of the present invention to provide an improved circuit for the suppression of bounce in a key-operated musical instrument of the type described.
A further object is to provide such an improved circuit wherein all the various gates are driven by a common supply voltage.